Checkpoint web-player design-system refactor and backend track genre tagging

Advances the ongoing token/componentization cleanup (anchored player dock,
border-based panels instead of floating shadows, corrected light-mode
accent/gradient tokens) alongside in-progress backend support for track
genre tags.

backend/Core/Musify.Application/Tracks/GetTracksByUserId.cs

@@ -27,6 +27,7 @@ namespace Musify.Application.Tracks
             var tracksQuery = database.UserHasTracks
                 .AsNoTracking()
                 .Include(ut => ut.Track.Owner)
+                .Include(ut => ut.Track.Tags)
                 .Where(p => p.UserId == request.UserId);
 
             if (!string.IsNullOrEmpty(request.Name))